• Korean Journal of Materials Research
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• v.33 no.12
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• pp.525-529
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• 2023

β-Ga₂O₃ has become the focus of considerable attention as an ultra-wide bandgap semiconductor following the successful development of bulk single crystals using the melt growth method. Accordingly, homoepitaxy studies, where the interface between the substrate and the epilayer is not problematic, have become mainstream and many results have been published. However, because the cost of homo-substrates is high, research is still mainly at the laboratory level and has not yet been scaled up to commercialization. To overcome this problem, many researchers are trying to grow high quality Ga₂O₃ epilayers on hetero-substrates. We used diluted SiH4 gas to control the doping concentration during the heteroepitaxial growth of β-Ga₂O₃ on c-plane sapphire using metal organic chemical vapor deposition (MOCVD). Despite the high level of defect density inside the grown β-Ga₂O₃ epilayer due to the aggregation of random rotated domains, the carrier concentration could be controlled from 1 × 10¹⁹ to 1 × 10¹⁶ cm^-3 by diluting the SiH4 gas concentration. This study indicates that β-Ga₂O₃ hetero-epitaxy has similar potential to homo-epitaxy and is expected to accelerate the commercialization of β-Ga₂O₃ applications with the advantage of low substrate cost.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.138-138
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• 2009

Al, Ga and In doped ZnO thin film were prepared by faing targets sputtering as a function of oxygen gas contents at R.T. Base pressure was $2{\times}10^{-6}torr$, and working pressure was 1mTorr. The properties of thin films on the electrical and optical properties of the deposited films were investigated by using a four-point probe (Chang-min), a Hall Effect measurement (Ecopia) and an UV/VIS spectrometer (HP). The minimum resistivities of AZO, GZO and IZO thin film were $6.5{times}10^{-4}[{\Omega}-cm],5.5{\times}10^{-4}[{\Omega}-cm]$ and $4.29{\times}10^{-4}[{\Omega}-cm]$. The average transmittance of over 80% was seen in the visible range.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.244.1-244.1
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• 2013

The p-type GaN which act as a hole injection layer in GaN-based LEDs has fundamental problems. The first one arises from the difficulty in growing a highly doped p-GaN (with a carrier concentration exceeding ~1018 $cm^{-3}$). And the second one is the absence of appropriate metals or conducting oxides having a work function that is larger than that of p-type GaN (7.5 eV). Moreover, the LED efficiency is decreases gradually as the injection current increases (the so-called 'efficiency droop' phenomenon). The efficiency droop phenomenon in InGaN quantum wells (QWs) has been a large obstacle that has hindered high-efficiency operation at high current density. In this study, we introduce the new approaches to improve the light-output power of LEDs by using graphene oxide sheets. Graphene oxide has many functional groups such as the oxygen epoxide, the hydroxyl, and the carboxyl groups. Due to nature of such functional groups, graphene oxide possess a lot of hole carriers. If graphene oxide combine with LED top surface, graphene oxide may supply hole carriers to p-type GaN layer which has relatively low free carrier concentration less than electron concentration in n-type GaN layer. To prove the enhancement factor of graphene oxide coated LEDs, we have investigated electrical and optical properties by using ultra-violet photo-excited spectroscopy, confocal scanning electroluminescence microscopy.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1360-1363
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• 2006

A borate compound was adopted as new host material for $EU^{3+}$ activator. The $Eu^{3+}-doped\;YCa_3(GaO)_3(BO_3)_4$ (YCGB) phosphors were successfully synthesized. Also, their photoluminescence properties under the excitation of UV ray were measured. In the XRD patterns of the synthesized powders, most peaks were well-matched to a gaudefroyite phase. The emission of $Eu^{3+}$ in YCGB consists of a strong peak centered at 622 nm, which is attributed to $^5D_O-^7F_2$ transition of $Eu^{3+}$ and several weak peaks at near the wavelength. Optimum $Eu^{3+}$ concentration of the red phosphor under the excitation with the wavelength of 395 nm was about 75 mol%. This indicates that the red phosphor has a relatively higher critical concentration than that of the other $Eu^{3+}-doped$ phosphors. The dominant interaction character of $Eu^{3+}$ might be dipole-dipole interaction.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.88-88
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• 2008

In this study, effect of thickness on structural, electrical and optical properties of B doped ZnO:Ga (GZOB) films was investigated. GZOB films were deposited on glass substrates by DC magnetron sputtering. The thickness range of films were from 100 nm to 600 nm to identified as increasing thickness, stress between substrate and GZOB film. The average transmittance of the films was over 80 % until 500 nm. Then a resistivity of $9.16\times10^{-4}\Omega$-cm was obtained. We presented that a GZOB film of 400 nm was optimization to obtain a high transmittance and conductivity.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.3
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• pp.215-218
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• 2011

A novel design of gas sensor using Ga-doped ZnO (GZO) thin films which are deposited on low temperature co-fired ceramic (LTCC) substrates is presented. The LTCC substrates with thickness of 400 ${\mu}m$ are fabricated by laminating 12 green tapes which consist of alumina and glass particle in an organic binder. The GZO thin films with different thickness are deposited on LTCC substrates, by RF magnetron sputtering method. The microstructure and sensing properties of GZO gas sensing films are analyzed as a function of the film thickness. The films are well crystallized in the hexagonal (wurzite) structure with increasing thickness. The maximum sensitivity of 3.49 is obtained at 100 nm film thickness and the fastest 90% response time of 27.2 sec is obtained at 50 nm film thickness for the operating temperature of $400^{\circ}C$ to the $NO_2$ gas.

• Journal of the Korean Ceramic Society
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• v.41 no.8
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• pp.623-627
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• 2004

Phase formation and electrical conduction behavior of Ba-doped LaBaGa $O_4$ layered perovskite were studied. Orthorhombic single phase of $K_2$Ni $F_4$-type structure was observed for the composition range of 0$\leq$x$\leq$0.2 in the La$\_$1＋x/Ba$\_$1＋x/Ga $O_4$$\_$4-$\delta$/ system by X-ray analysis. In the dry atmosphere, La$\_$0.8/Ba$\_$1.2/Ga$\_$3.9/ exhibited mixed conduction of oxygen ion and hole (p-type) at high p( $O_2$). However, in water vapor containing atmosphere, it showed proton conduction due to the incorporation of water into oxygen vacancies. As the temperature decreased, the contribution of proton conductivity to the total conduction increased and proton conduction was dominant below 350$^{\circ}C$. The activation energy for proton conduction was calculated as 0.72 eV.

• Journal of IKEEE
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• v.22 no.2
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• pp.427-431
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• 2018

This research was worked about $Ga_2O_3$ Epi wafer that was one of the mose wide band gap semiconductors to be used power semiconductor industry. This wafer was grown $5.3{\mu}m$ thickness on Sn doped $Ga_2O_3$ Substrate by HVPE(Hydride Vapor Phase Epitaxy). Generally, we can fabricate 600V class power semiconductor devices when the thickness of compoound power semiconductor is $5{\mu}m$. but in case of $Ga_2O_3$ Epi wafer, we can obtain over 1000V class. As a result of J-V measurment of the grown $Ga_2O_3$ Epi wafer, we obtain $2.9-7.7m{\Omega}{\cdot}cm^2$ on resistance. Specially, in case of reverse, we comfirmed a little leakage current when the reverse voltage is over 200V.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07b
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• pp.955-959
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• 2004

The effects of conduction band offset on 2 dimensional electron gas (2DEG) in N-InAlAs(AlAsSb)/InGaAs/InAlAs (AlAsSb) metamorphic heterostructures (MMHS) are studied. A combination of the Shubnikov-deHaas oscillations and the Hall measurements is used to investigate the electron transport properties of these structures. The mobility in the second subband is higher than that in the first subband in all heterostructures. This is attributed to the fact that electrons in the first subband we, on average, closer to the interface and are therefore scattered more strongly by ionized impurities. The results suggest that intersubband scattering rate is more dominant in structures with higher conduction band offset whereas alloy scattering is found to be more dominant in the higher band offset system.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2002.11a
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• pp.81-84
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• 2002

The effects of the isoelectronic AI-doping of GaN grown by metal organic chemical vapor deposition were investigated for the first time using scanning electron microscopy (SEM), Hall measurements, photoluminescence (PL), and time-resolved PL. When a certain amount of Al was incorporated into the GaN films, the room temperature photoluminescence intensity of the films was approximately two orders larger than that of the undoped GaN. More importantly, the electron mobility significantly increased from 130 for the undoped sample to $500\textrm{cm}^2/Vs$ for the sample grown at a TMAl flow rate of $10{\mu}mol/min$, while the unintentional background concentration only increased slightly relative to the TMAl flow. The incorporation of Al as an isoelectronic dopant into GaN was easy during MOCVD growth and significantly improved the optical and electrical properties of the film. This was believed to result from a reduction in the dislocation-related non-radiative recombination centers or certain other defects due to the isoelectronic Al-doping.